In a hydraulic brake booster a piston is slidably mounted within a housing and is pressure responsive to move relative to the housing whereby the piston operatively engages a brake master cylinder to effectuate a brake application. In order to move the piston into engagement with the master cylinder, the piston cooperates with the housing bore to form a pressure chamber. The piston includes inlet and outlet openings for communicating fluid therethrough and a valve member is slidably mounted within a bore on the piston to communicate fluid to the pressure chamber which pressure urges the piston into engagement with the master brake cylinder to effectuate a brake application.
The valve member includes a land which cooperates with the piston bore to communicate the inlet opening with the pressure chamber when an operator actuator is actuated to move the valve member within the piston bore. Consequently, the valve member land operates as a metering valve controlling high pressure flow to the pressure chamber. As a result, a substantial pressure drop occurs across the land which generates an undesirable audible noise.
It is desirable to provide a hydraulic brake booster with a valve member that is slidably mounted within the piston bore to communicate pressurized fluid to the pressure chamber and that is also provided with a metering land which cooperates with the piston bore to quietly communicate the pressurized fluid to the pressure chamber.